Power and heat can be produced by combustion of hydrocarbons, e.g., including fossil and synthetic fuels. Air is a readily available source of the oxygen required in combustion reactions. However, it can be difficult to protect the environment from greenhouse gases, e.g., carbon dioxide, produced in air-based combustion reactions.
Reduction/oxidation (redox) reactors address this problem by providing for inherent carbon-dioxide capture. In a redox system, power is generated by oxidizing metal particles to yield metal-oxide particles. The metal-oxide particles can then be reduced in a reduction reaction with hydrocarbon fuel for use in a next redox cycle. The oxidation reaction does not produce carbon dioxide. The reduction reaction yields carbon dioxide and steam. The steam can be readily separate out so that the carbon dioxide can be isolated and captured.
In a batch-cyclic redox reactor system, a batch-cyclic reactor alternates between an air mode and a fuel mode. In air mode, oxidation particles are oxidized, generating heat. In fuel mode, the oxidation particles are reduced without generating much heat. So that heat can be generated continuously, two or more batch-cyclic redox reactors can be operated out-of-phase with respect to each other so that at least one is in air mode at any given time.
However, the volume of gas needed during air mode is three to seven times the volume needed during fuel mode. This can be a challenge for reactors that rely on fluid flow to fluidize the oxidization particles to improve reaction characteristics. An alternative is to use additional reactors, e.g., so that three can be in air mode while one is in fuel mode. However, this considerably increases the entry cost for a redox reactor system.
A continuous-loop combustion (CLC) reactor system combines a reactor dedicated to reduction with a reactor dedicated to oxidation. Oxidation particles are continuously shuttled (looped) back and forth between the oxidation reactor and the reduction reactor so that heat generation can continue uninterrupted. The oxidation reactor can be design to provide whatever air flow is required to match the reduction rate of the reduction reactor. However, the equipment required to shuttle the oxidation particles between the oxidation and reduction reactors places a heavy burden on the entry cost for a redox reactor system.
What is needed is a combustion reactor that is both green and economical for moderately-sized installations. More specifically, what is needed is a more economical moderate-power redox reactor system.